Method for the manufacture of gas conditioning packing



April 9, 1968 c. G. MUNTERS 3,377,225

METHOD FOR THE MANUFACTURE OF GAS CONDITIONING PACKING OOO /OOO

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Filed April 25, 1965 INVENTOR CARL GEORG MU N TERS ATTORNEY UnitedStates Patent Ofiice 3,377,225 Patented Apr. 9, 1968 3,377,225 METHODFOR THE MANUFACTURE OF GAS CONDITIQNING PACKING Carl Georg Munters, 3Danderydsvagen, Stocksund, Sweden Continuation-impart of applicationSer. No. 202,333,

June 13, 1962. This application Apr. 25, 1966, Ser.

8 Claims. (Cl. 156210) ABSTRACT OF THE DISCLOSURE Heat and/or moisturetransfer laminated corrugated bodies for-med of an alternate lamina of acorrugated layer with a plane layer of sheets of asbestos, cohered andcured by impregnating the fiber with inorganic particles and which, fortemporary assembly purposes may also contain organic fibers as well asorganic adhesive, and the assembled body is heated to fuse the inorganicparticles into a permanent body between asbestos fibers of greatstrength and stability, preferably set by oxidizing the corrugated bodyin a stream of air at a controlled rate so that only sufiicient heat isprovided to fuse the inorganic particles but insufficient to expel waterof crystallization from the asbestos fiber, thereby avoiding chemicaldestruction of the asbestos fiber.

This application is a continuation-in-part of copending application Ser.No. 202,333, filed June 13, 1962, and now abandoned.

The present invention relates to a method for the preparation of aninorganic fibrous heat and moisture transfer body having parallel gaspermeable cells extending across the body. More particularly, thepresent invention relates to a method for bonding and heat-curing aninorganic fibrous cellular body with fused particles of an inorganicbonding material at temperatures controlled to fuse said bondingparticles and impart substantial bonded fibrous structural strength andstability characteristics to the cellular body.

In the preparation of heat and moisture transfer bodies it is desirableto use thin-walled fibrous sheets of inorganic fibers such as asbestos,assembled and firmly bonded into a laminate by spiral winding or as arectangular block, and having gas permeable cel-ls extending parallelrom one side of the body to an opposite side for easy gas flowtherethrough. The body of laminated inorganic fibrous sheets such as ofasbestos in use for heat and moisture transfer systems have gasespassing through different body portions to absorb moisture in oneportion and expel it from another portion, each body portion being at asubstantial temperature differential from the other. The cellular bodyis sometimes impregnated with a desiccant substance such as silica gelor lithium chloride to enhance its moisture-transfer capacity.

The fibrous cellular body, variable with the particular compositionmaterials, is subjected to temperatures ranging from about 200 to about700 C. for regeneration, and this is usually in the presence of airwhich may supply uncontrolled oxidation and not only destroy organicmaterials contained in such body, but can release excessive heat tomelt, fuse or chemically destroy the structural strength of some fibrousmaterials. For instance, at temperature of about 1000 C., asbestosfiber, a preferred fibrous material for use in this invention, will losewater of hydration and be converted to a weak, easily-powdered materialwhich is undesirable for present purposes. For these reasons theinorganic materials for bonding must fuse or melt at the curingtemperature.

According to the present invention an inorganic fibrous material such asasbestos, before or after forming into sheets, is treated with a waterinsoluble suspension of inorganic binder materials with or withoutfurther addition of temporary organic binder materials. The sheets arethen assembled, usually after corrugating and temporarily bonding into acellular body as described, or such preformed cellular body may beimpregnated or coated with the inorganic binder material and the driedstructure is then heat-cured. The green or uncured assembled structurecontaining inorganic binder with or without an organic binder is thenheatcured by heating the assembled body to a critical fusion temperatureof the inorganic binder material, a temperature sufficient to fuse theinorganic particles and thus effect a bond between the inorganic fibers,but at a temperature below that at which the inorganic fibers aredamaged or destroyed. Such temperature control is effected according tothe present invention by heating while circulating gas through theporous structure at a rate and containing only sufficient oxygen torelease a limited quantity of heat and thus to allow close temperaturecontrol for oxidation of the organic materials present in the structure.Thus, the heat-curing operation effects the inorganic bonding in thepresence of the circulating gases controlled to destroy any organicmaterials present at a temperature controlled below that at which theinorganic fibrous structure is destroyed or damaged; and in the case ofasbestos fibers specifically, below that temperature at which water ofcrystallization will be evolved from the asbestos fiber.

By the practice of the present invention, inorganic fibrous materialsmay be cured into strong, thin-walled cellular bodies having gaspermeable cells extending in the axial direction of the structure andsubstantially gasimperrneable walls extending in the radial direction.

It is an object of this invention, therefore, to provide a method forheat-curing to bond a raw cellular structure of a non-metallic inorganicfibrous base material with an inorganic bonding agent.

It is another object of this invention to provide a method forheat-curing an inorganic fibrous base material having a rugged heat andmoisture-resistant cellular structure particularly adapted to transferof heat and/ or moisture under extreme temperature changes over extendedperiods of time.

It is yet another object of this invention to provide a method for heatcuring a thin-walled cellular body in an atmosphere of heatedoxygen-containing gas which is passed through the cellular structuresuch that residual organic materials within the inorganic fibrous basemay be oxidized Without ignition.

It is a further object of this invention to provide a method for themanufacture of a heat and/or moisture transfer body having an inorganicfibrous base bonded by fused inorganic particles into a strong,thin-walled cellular body having gas-permeable cells extending in anaxial direction and substantially gas-impermeable walls of the cellsextending in a radial direction and which may contain a coating of ahygroscopic substance for transfer of moisture to a hot stream of fluidsuch as air or other gas.

These and other objects and advantages of the present invention willbecome more readily apparent from the following detailed description ofthe invention taken in con junction with the drawings in which:

FIG. 1 is a side elevational view of a heat-curing kiln useful forcarrying out the method of the present invention; and

FIG. 2 is a partial top-elevational view of the cured, thin-walledcellular body illustrated in larger scale than the correspondingcellular body being cured in the kiln of FIG. 1.

In the method of the present invention a cellular body composed of aninorganic fibrous base material containing organic residuals is formedinto thin sheets of a thickness not exceeding about $3 millimeter. Thethickness of these sheets for the cellular body walls, althoughdesirably not exceeding about millimeter, need only be limited by thestrength characteristics desired in the final structure since it isrecognized that the effectiveness of the transfer system for thetransfer of moisture and/or heat per unit time is dependent on the wallthickness.

It is sometimes desirable to add a combustible organic adhesive to theinorganic base material either to the batch of material prior to theformation of the thin sheets or as a coating on the preformed sheets, oreven to the laminate thereof as it is being formed to allow preliminarybonding to a stable assembly. The amount of adhesive added to theinorganic base material is sufiicient for support of the cellular wallsin the uncured state although limited to an amount which may becontrollably oxidized and removed during the heat-curing operation. Thecombustible organic adhesive usefully added to the uncured fibrous basematerial includes common commercial adhesive substances such as starch,casein, soya protein or the like. Other simi lar organic materials maybe separately added or the adhesive materials may be added incombination if desired.

In forming the cellular body it is sometimes useful to include somecombustible cellulose fiber admixed with the inorganic fiber in theuncured state and prior to formation of the thin sheets; or celluloseintermediate sheets maybe included in the laminated assembly as it isformed. The cellulose fiber being combustible is destroyed by thecontrolled combustion during the curing of the assembled inorganicfibrous body.

Although the thin-walled cellular body may be formed in any desiredconfiguration, it is desirable that the structure be formed by cohesionof corrugated sheets of thinwalled base inorganic fibrous materialdisposed as a laminate or in a circular or ovular pattern. Rectangularlaminated configurations of the thin-walled base material wherein thecorrugated layers are disposed in parallel relationship may also beformed if desired.

The inorganic fibrous materials forming the base of the cellular bodymay be exemplified by asbestos filaments having extremely finediameters. These filaments may be reenforced by an inorganic binder suchas powder of enamel which serves as an adhesive for the asbestosfilaments after the cellular body has been heat cured. The appliedpowder of enamel desirably has a powder consistency approximate to thatof flour and may be suspended in a liquid such as water, alcohol or thelike which readily evaporates during the heat-curing or enamel fusingoperation. The power of enamel may be applied tothe inorganic filamentsduring the blending of the base such that the base is effectivelyimpregnated with the powder of enamel prior to the fusing operation.Alternate methods for applying the powder of enamel such as by spray,brush-coating or the like may also be used for application of enamel tothe asbestos filaments if desired.

After the asbestos base has been formed in the thinwalled cellularconfiguration, the uncured assembly is heated while an atmosphere ofoxygen-containing gas exemplified by air is passed through the cellularstructure. The fibrous base material is subjected to a heat-curingtemperature sufficiently high for fusion of the enamel for bonding ofthe fibers to result. Practically, the fibrous base material isheat-cured at a temperature in the neighborhood of above 200 C. andbelow the temperature at which water of hydration is expelled from theasbestos fibers.

During the heat-curing operation, it is necessary that the organiacmaterials in the asbestos base be slowly oxidized and rendered heatstable. Due to the low ignition temperatures of the organic materials,improper heatcuring of the cellular body may disintegrate the asbestosfibers to fine powders such that the affected areas have reducedstrength characteristics. Accordingly, the heatcuring operation isperformed such that the organic materials or the asbestos base arecontrollably oxidized by passing an atmosphere of oxygen-containinggases through the cellular structure. The volume of theoxygen-containing gas passed through the cellular structure per unit oftime is sufficient to prevent the development of hot spots by theuncontrolled oxidation of the organic materials within the asbestosbase. Uncontrolled oxidation of the organic materials may be limited byadjusting either the volume or the oxygen content of the gases beingpassed through the cellular structure. It is important, therefore, thatthe organic materials in the asbestos base be oxidized under controlledconditions when the thin-walled configuration is heat cured.

The asbestos fiber base formed as a thin-walled cellular configurationmay serve as a support for a hygroscopic substance as a desiccant saltexemplified by lithium chloride, magnesium chloride, calcium chloride orthe like. The cellular body may, if desired, be coated with water glasssuch as sodium or potassium silicate, and the silica may be precipitatedon the walls of the cellular body as silica gel by treatment with acidor various precipitating salts to leave a highly porous, absorbentprecipitate of silica gel on the cellular walls after drying.Alternately, the thin-walled cellular body may be prepared forhumidification of gases by coating the cellular walls with a thin filmof an aqueous humectant illustrated by Water containing a polyhydricalcohol such as ethylene glycol, glycerol, or lower glycol ethers.

The quantity of hygroscopic substance applied to the fibrous base may beregulated and limited such that the asbestos fibers retain some degreeof capacity to absorb moisture. However, should the thin-walled cellularbody he intended solely for heat transfer purposes, a coating cover ofenamel may be applied on the thin walls as a hard, coherent layer inwhich case the body becomes highly non-hygroscopic.

Advantages may also result by application of a coherent layer of enamelto one surface layer of the thin-walled cellular body to increase thehardness of the overall structure while retaining the hygroscopic natureof the opposite surface thereof. The resulting structure thus formed isone having a non-hydroscopic surface and a hygroscopic surface.

Referring next to the drawing, kiln 10 is illustrated having structuralwalls made of any suitable heat insulating material. Formed in one ofthe walls of kiln 10 is inlet opening 12 and outlet opening 14, eachprovided with damper 16 and 18, respectively, or similar fluidthrottling device. Kiln 10 encloses inner casing 20 formed of sheetmetal or similar material defining chamber 22. Positioned within chamber22 is screen 24 which serves as a platform to support cellular body 26placed thereon for the heat-curing operation. The portion of screen 24not covered by cellular body 26 may be covered by shield 28 to insurethat substantially all the oxygen containing gas. such as air passingthrough screen 24 also passes through cellular body 26. Perforated plate30 may be disposed below screen 24 to uniformly distribute the oxygencontaining gas over the cross-section of chamber 22. Heater 32 providesa heat source for heating the gaseous medium which is circulatedupwardly through chamber 22 and downwardly past heater 32 by means offan 34 driven by motor 36 through shaft 38.

Cellular body 26 is preferably composed of thin sheets of asbestos whichare corrugated or formed in a suitable configuration such that thesheets bear against one another only at mutually-spaced intervals toform cells for passage of heated fluids through the configuration in anaxial direction with substantially no gas passage in a radial direction.

In the embodiment of the invention illustrated in FIG. 2, cellular body26 is composed of alternately disposed plane sheets 40 which may bejoined to corrugated sheets 42 by adhesive-containing contact areas. Thespacing between plane sheets '40 is desirably less than 3 millimetersand preferably about between 1 or 2 millimeters.

The necessary strength may be imparted to the uncured asbestos sheets byaddition of a combustible organic adhesive such as starch and, ifdesired, the addition of a minor quantity of cellulose fiber usuallymixed with the asbestos fibers. The asbestos base may also contain, inaddition to cellulose fibers, a fine powder of inorganic bondingmaterial such as powder of enamel which may be applied to the asbestossheets as previously described. The powder of enamel is fused and bondsthe asbestos fibers together during the heat-curing operation which alsocontrollably oxidizes the combustible organic adhesive used in theuncured asbestos assembly.

The oxygen-containing gases circulating within kiln are heated by heater32 to a temperature between about 200 C. and about 600 C., andpreferably about 300 C. and about 500 C, The temperature of the gasescirculating Within kiln 10 must be regulated to fuse the powder ofenamel and controllably oxidize the organic materials within cellularbody 26 without destroying the asbestos fibers therein. The temperatureof the circulating gases as Well as the oxygen content thereof may beadjusted by addition of make-up air into kiln 10 through inlet 12 whilea corresponding quantity of gas is permitted to escape through outlet14.

During the heat-curing operation, the volume of gas circulating withinkiln 10 per unit of time may be adjusted to control oxidation of theorganic materials while permitting fusion of the powder of enamel at atemperature below that which will cause release of water of hydrationfrom the asbestos fibers. The volume of gas passed through the cells ofthe cellular body therefore limits the development of uncontrolledoxidation areas in the thin walls of the transfer body being cured.After the transfer body has been heat-cured, the thin sheets forming thewalls of the cellular body are held to one another primarily by thefused enamel.

When cellular body 26 is to be used for dehydration purposes, the wallsof the body may be coated with a hygroscopic substance such as lithiumchloride or the like suitably applied after the heat-curing operation iscompleted. It is also possible to coat the asbestos fibers prior to theheat-curing operation with a metallic material in powder form ofselected fusion points which fuse and reinforce the thin-walled asbestossheets. The nondesired oxidation of such metals may be prevented byperforming the heat-curing operation in an atmosphere containing a largepercentage of reducing or inert gases which limit oxidation of themetals.

It will be understood that various changes may be made in the details ofthe present invention as hereinbefore described without departing fromthe spirit of the invention as defined by the appended claims.

What is claimed is:

1. The method of forming a transfer body useful for heat, moisture, andboth heat and moisture transfer comprising mixing heat decomposableinorganic asbestos fibers with water insoluble inorganic bondingparticles fusible at a temperature substantially below the temperatureof decomposition of said asbestos fiber, forming the mixed fibers andinorganic bonding particles into a corrugated laminated structurealternately plane and corrugated thin-walled sheets each lamina coheredto the adjacent layer of the laminate and spaced to maintain the depthof the corrugations, thereby providing a plurality of gas permeablechannels passing coaxially from side to side of the laminated structurethus formed, and heating said structure to a temperature only sufiicientto fuse the inorganic binder particles and below the temperature ofdecomposition of said fibers and in the range of 200 to 700 C. andthereby bond the inorganic fibers into a mechanically and structurallystrong transfer body.

2. The method of forming a transfer body as defined in claim 1 whereinthe inorganic asbestos fibers are treated with both inorganic fusibleparticles and temporary organic adhesive, the coated fibers are thenassembled into said corrugated laminated structure and the structure isthen heated sufficiently to fuse said inorganic particles and bond theinorganic fibers into a stable structure, the applied heat beingcontrolled by passing a gas through the corrugated laminated structureof said body, said gas containing sufficient oxygen to slowly oxidizethe temporary organic adhesive at a temperature in the range notsubstantially in excess of that necessary to fuse said inorganic fusibleparticles and less than that sufficient to damage said inorganic fiber.

3. The method of forming a transfer body as defined in claim 2 whereinthe inorganic fibers further contain organic fibers which are oxidizedwith the temporary organic adhesive at a temperature controlled toeffect fusion of said inorganic particles and less than sufficient todamage said inorganic fiber.

4. A method for the manufacture of a transfer body which comprisesforming an asbestos base material as a thin-walled cellular body oflaminated structure comprising a corrugated asbestos fiber sheetalternating with a plane asbestos fiber sheet providing a plurality ofgas permeable channels extending from one side to the opposite side inan axial direction and substantially gas impermeable walls extending inthe radial direction, said thinwalled cellular body having adjacentwalls adhering to one another by a temporary organic adhesive coatingsaid body with a solid inorganic binder substance fusable below about700 C., heating the thin-walled cellular body to a temperature aboveabout 200 C. sufficient to fuse said inorganic coating, but below about700 C., the temperature at which water of hydration is expelled fromsaid asbestos base while passing an oxygen-containing gas through thegas-permeable cells extending in the axial direction whereby the fibrousinorganic base is heat-cured with substantial bonding of the inorganiccoated fibrous structure.

5. A method for the preparation of an asbestos transfer body havingparallel gas-permeable cells extending through the transfer body whichcomprises, blending an asbestos material with both an inorganic and anorganic adhesive material to form a fibrous base, forming thinwalledsheets of said fibrous base, assembling the thinwalled sheets as alaminated cellular body of alternately plane and corrugated sheetscomprising a corrugated laminate, each corrugated lamina thereof adheredto an adjacent plane layer, serving to space corrugated layers, therebyproviding gas permeable cells extending from one side to an oppositeside in-an axial gas flow direction and substantially gas-impermeablewalls extending in a radial direction, passing an oxygen-containing gasat a temperature between about 200 and 700 C. through the gas-permeablecells to fuse said inorganic adhesive and for the controlled oxidationof organic materials within the fibrous base whereby the fibers of thebase are bonded together in the assembled transfer body.

6. The method of forming a transfer body for heat, moisture and bothheat and moisture, comprising forming a laminated structure ofalternately plane and corrugated thin sheets of asbestos fibers having aplurality of parallel gas permeable channels passing from side to sideof the laminated structure, evently distributing a solid fusibleinorganic substance over said fibers and heating said structure to atemperature only sufficiently high to fuse said substance, and then toset the same on the fibers without destroying said fiber in the range of200 to 700 C., thereby imparting a high mechanical strength to the body.

7. The method of forming a transfer body as defined in claim 6 whereinthe inorganic fibers in sheet form are first formed into the saidcorrugated laminated structure, and the body is then coated with asuspension of said water insoluble inorganic bonding particles, saidbonding particles being set on said fibers by heating to about thefusion temperature of said particles.

8. The method of forming a transfer body useful for heat, moisture andboth heat and moisture transfer, comprising mixing together asbestosfibers, combustible and heat decomposable organic adhesive, andinorganic enamel powder adhesive to provide a fibrous base sheetmaterial, corrugating said sheet material and bonding a plurality ofsaid corrugated sheets together, subjecting said corrugated sheets to aheat curing temperature of between 200 to 700 C. in an oxygen-containingatmosphere whereby the enamel becomes fused and bonds the asbestosfibers together in said corrugated sheets, and the organic materialscontained therein are oxidized and destroyed without affecting theasbestos fibers.

References Cited UNITED STATES PATENTS 9/1934 Toohey et al. 1611565/1951 Stafford 161205 7/ 1954 Ecker't et a1 161205 2/1955 Spooner161205 10/1957 Heyman 156-155 1/1966 Munters 11746 5/1961 Kramig 161137FOREIGN PATENTS 9/ 1922 Great Britain.

5 MORRIS, SUSSMAN, Primary Examiner.

